The Royal Marines have launched an operation to secure an area in turbulent south-eastern Afghanistan.

It comes about two weeks before next month's grand tribal council, which will choose a new transitional government in the country.

More than 300 troops have been deployed over the last three days for Operation Buzzard, which is expected to last for up to a month.

They are attempting to make secure the area south of the mountainous Khost region, down to the
border with Pakistan.

It is potentially the most dangerous operation so far

BBC defence correspondent Paul Adams

The operation aims "to prevent
freedom of movement of al-Qaeda and Taleban and to deny them
sanctuary from which to operate," spokesman Lieutenant Colonel Ben Curry said.

The marines will be setting up checkpoints and conducting foot, vehicle and helicopter patrols around villages in what has been described as a "sensitive" and "lawless" region.

BBC defence correspondent Paul Adams said Operation Buzzard would be much more visible than the marines' three previous operations in Afghanistan, and was "potentially the most dangerous operation so far".

"We will see the men of 45 Commando conducting a variety of operations which will bring them into contact with the people of Afghanistan much more than we've seen up to now.

'Execution' fears

"They are going to come into contact with more warlords, smugglers, all manner of elements which have not yet come into contact with coalition forces, who may not understand why the Royal Marines are down there."

Defence officials believe al-Qaeda and Taleban forces, operating in small groups on either side of the border, could be planning terrorist attacks to disrupt the political process.

One marine told the AFP news agency opposition fighters were seeking "some kind of
symbolic victory over the coalition forces".

They could try to "down a helicopter, capture a member of the
coalition and subject them to a public execution - something of
that nature is quite possible".

He said the area was renowned for "voluble warlords" who had checkpoints of their own, and would be very unhappy at the presence of the marines.

The marines have been deploying at night for three days

Major Richard King of 45 Commando said it could be quite difficult to identify the enemy.

"The terrorist organisations have really filtered back into the population, and are not easily identifiable.

"So as we do in Northern Ireland, we patrol to bring the locals on-side, but also gain intelligence against the terrorist organisations. Then we can isolate them and strike them."

Several US civil affairs officials will accompany the marines around the area, on a "hearts and minds" operation looking at issues such as water and power supplies.

Troops will rotate from among the 1,700 marines based at Bagram, the country's main air base, further north.

'No safe sanctuary'

Brigadier Roger Lane, the current leader of the marines, has made a radio address transmitted in
Pashtu and Farsi to explain why the troops are there, and "reassure the people
this is not a fight against Islam".

He said in the broadcast that the coalition had "no long-term strategic ambition of staying in Afghanistan".

"We will search mountains and other areas to ensure terrorists
have no safe sanctuary," he said.

The marines have not yet had any major engagements with enemy fighters, despite their three operations.

"They are there, but they are not coming out to fight," one marine told news agency Reuters.